Fix inconsistent IS_ERR and PTR_ERR in cifs_find_swn_reg(). The proper
pointer to be passed as argument to PTR_ERR() is share_name.
This bug was detected with the help of Coccinelle.
Fixes: bf80e5d4259a ("cifs: Send witness register and unregister commands to userspace daemon") Signed-off-by: YueHaibing <yuehaibing@huawei.com> Reviewed-by: Samuel Cabrero <scabrero@suse.de> Signed-off-by: Steve French <stfrench@microsoft.com>